Production of hydrofluoroalkanes

Abstract

A process for the co-production of two or more hydrofluoroalkanes which comprises contacting an alkene or a halogenated alkane with hydrogen fluoride at elevated temperature in the presence of a fluorination catalyst to produce a first hydrofluoroalkane and wherein an organic precursor to a second hydrofluoroalkane is provided in the process whereby to produce a second hydrofluoroalkane in addition to the first hydrofluoroalkane. In particularly preferred embodiments of the process, the first hydrofluoroalkane is 1,1,1,2-tetrafluoroethane derived from 1-chloro-2,2,2-trifluoroethane or trichloroethylene and the second hydrofluoroalkane is one or more of pentafluoroethane, difluoromethane and 1,1,2,2-tetrafluoroethane.

We claim: 
     
       1. A process for the production of hydrofluoroalkanes which comprises contacting trichloroethylene with hydrogen fluoride at elevated temperature in the presence of a fluorination catalyst to produce 2-chloro-1,1,1-trifluoroethane and contacting the 2-chloro-1,1,1-trifluoroethane with hydrogen fluoride at elevated temperature in the presence of a fluorination catalyst to produce 1,1,1,2-tetrafluoroethane wherein the reactions between trichloroethylene and hydrogen fluoride and between 2-chloro-1,1,1-trifluoroethane and hydrogen fluoride are carried out in separate reaction zones and wherein the precursor to a second hydrofluoroalkane is added to the process in the reaction zone wherein the 2-chloro-1,1,1-trifluoroethane and hydrogen fluoride are reacted to produce a second hydrofluoroalkane in addition to the 1,1,1,2-tetrafluoroethane and the 1,1,1,2-tetrafluoroethane and second hydrofluoroalkane are recovered. 
     
     
       2. A process as claimed in claim 1 which comprises the steps of: (A) contacting a mixture of 1,1,1-trifluoro-2-chloroethane and hydrogen fluoride with a fluorination catalyst at a temperature in the range from about 280° C. to about 450° C. in a first reaction zone to form a product containing 1,1,1,2-tetrafluoroethane and hydrogen chloride together with unreacted starting materials,   (B) passing product of step (A) together with trichloroethylene to a second reaction zone containing a fluorination catalyst at a temperature in the range from about 200° C. to about 400° C. but lower than the temperature in step (A) to form a product containing 2-chloro-1,1,1-trifluoroethane, 1,1,1,2-tetrafluoroethane, hydrogen chloride and unreacted trichloroethylene and hydrogen fluoride,   (C) treating product of step (B) to separate 1,1,1,2-tetrafluoroethane and hydrogen chloride from 2-chloro-1,1,1-trifluoroethane, unreacted trichloroethylene and hydrogen fluoride, and   (D) feeding 2-chloro-1,1,1-trifluoroethane obtained from step (C) together with hydrogen fluoride to said first reaction zone (step A), wherein an organic precursor to a second hydrofluoroalkane is added to step (A) of the process whereby to form a second hydrofluoroalkane in addition to 1,1,1,2-tetrafluoroethane.   
     
     
       3. A process as claimed in claim 1 wherein the organic precursor to the second hydrofluoroalkane is an alkene or a halogenated hydrocarbon. 
     
     
       4. A process as claimed in claim 1 wherein the organic precursor to the second hydrofluoroalkane is generated in situ. 
     
     
       5. A process as claimed in claim 4 wherein the organic precursor to the second hydrofluoroalkane is generated by feeding chlorine to the process. 
     
     
       6. A process as claimed in claim 1 wherein the second hydrofluoroalkane is pentafluoroethane (HFA 125) and the organic precursor thereto is dichlorotrifluoroethane (HCFC 123) and/or chlorotetrafluoroethane (HCFC 124). 
     
     
       7. A process as claimed in claim 1 wherein the second hydrofluoroalkane is difluoromethane (HFA 32) and the organic precursor thereto is methylene chloride and/or chlorofluoromethane (HCFC 31). 
     
     
       8. A process as claimed in claim 3 wherein the organic precursor to the second hydrofluoroalkane is an alkene or a readily fluorinated halogenated alkane and is fed to the process together with the trichloroethylene. 
     
     
       9. A process as claimed in claim 3 wherein the organic precursor to the second hydrofluoroalkane is a less readily fluorinated halogenated alkane and is fed to the first reaction zone. 
     
     
       10. A process as claimed in claim 5 wherein the chlorine is fed to the first reaction zone. 
     
     
       11. A process as claimed in claim 10 wherein the chlorine is fed to the recycle stream to the first reaction zone. 
     
     
       12. A process as claimed in claim 11 wherein the chlorine is fed to the product stream after the second reaction zone but before the product separation step. 
     
     
       13. A process as claimed in claim 12 wherein a third reactor is provided in which the organic precursor to the second hydrofluoroalkane is generated. 
     
     
       14. A process as claimed in claim 1 wherein the relative proportion of trichloroethylene to organic precursor to the second hydrofluoroalkane is in the molar ratio of from about 1:1 to about 20:1. 
     
     
       15. A process as claimed in claim 1 wherein the fluorination catalyst is a zinc-promoted chromia catalyst.